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Colour Deficiency, and An Idea to Help

November 27th, 2008 · Posted by Hugo · 13 Comments

I’m colour deficient. (I’m explicitly *not* colour-blind.) No, I’m not sensitive about the matter, that’s more in jest. The origins of the distinction date back to Grade 1 though: I mention to friends in class:

“hey, I’m colour blind!”
they ask: “what colour’s this?”
“what colour’s that?”
“and this?”
“what about and that?”
“you’re not colour blind!”

Ha! Well, we were seven years old. What do you expect?

In any case, here’s my ‘lil invention, that I sadly haven’t implemented for myself: carry around a red and green filter. Or even a blue one as well, if you need it.

Colour Perception

Allow me to sketch an over-simplified way of how we see colour…

Our eyes are sensitive to “three colours”. But that isn’t actually true. They are sensitive to three ranges of colour. Suppose you see some yellow light, with wavelength 580 nanometer (abbreviated nm, that’s a millionth of a millimetre). This lies between the wavelength for red light and green light (620–750 nm and 495–570 nm respectively). Your eye does not get stimulated for “yellow”, it gets stimulated for red to the one side, and green to the other, which we then interpret as “yellow”. For this reason, and this reason alone, we can simulate yellow light with a computer or TV screen by combining red and green light. (Yes, red and green light together looks like yellow.)

The image above (source: Wikipedia) shows the wavelength sensitivities of our eye, notice the heavy overlap between red and green. Along the horizontal axis is the colour (according to the wavelength of the light), and the vertical is how each is perceived by the eye. It suggests that light that is right in the middle of our green-sensitivity still looks more than 80% red to our “red receptors”. Our brains or neural networks interpret something that stimulates “100% green” and “80% red” as green.

The Idea

Now to colour-blind people, it is often this distinction between red and green that they find hard to make. My idea is to externalise the filtering between red and green. A red filter (a piece of plastic that lets through red light, aka red plastic) will let through red light unhindered, while suppressing “not red” wavelengths, while a green piece of plastic lets through green light unhindered, suppressing the rest.

Again these filters will overlap, but the better you can get them to differentiate, the sharper you can make their graphs as mentioned above, the bigger their effect will be on the red and green light they let through. Under the pair of filters, red light should look dimmer on the green side, and green light should look dimmer on the red side.

Resistors, Rubik’s

Maybe something like this would help us poor colour-deficient people from telling apart different resistor values — in electronics the amount of resistance on a resistor is encoded by a couple of coloured lines. Maybe if I had these filters, I would have opted for hardware instead of software!

Naah, kidding, I got by. My deficiency isn’t too bad. It presents itself in a couple of interesting places, such as sometimes having to look twice to distinguish orange and yellow on a Rubik’s cube… while it sounds like most people find the orange to be closer to the red than to the yellow (?!) — what do you think?

Canon PowerShot woes!

The biggest evil though, the biggest handicap this is for me right now, is Canon. Yes, Canon. Canon is being evil towards us poor colour deficient people. I can not for the life of me determine whether my Canon PowerShot camera’s batteries have finished charging or not… the battery charge indicator is a mix between red/green or (or yellow/green for all I know?) representing charging/charged, and even after plugging out the battery and plugging it back in, to get the light to switch from charged back to charging, to have something to compare to, doesn’t help me! Sometimes, yes, I can determine the answer with suitable certainty, but these days I simply plug in the batteries for “long enough”. Which means it is impossible for me to charge three batteries in “as short a time as possible”.


I see a vague 21, or some other shapes if I search for them, but I can’t even point out where the 74 is suppose to be.

Further Reading (Wikipedia): Visible Spectrum, Colour Vision, Colour blindness


  • Simplified human cone response curves, based on Dicklyon’s PNG version, itself based on data from Stockman, MacLeod & Johnson (1993) Journal of the Optical Society of America A, 10, 2491-2521d (log E human cone response, via
  • Ishihara Plate 9 – public domain – You MUST NOT use this image in diagnostics.

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13 responses so far ↓

  • 1 Hugo // Nov 27, 2008 at 1:34 am

    Note: this post is a gross simplification. If anyone cares to fill in the details in comments, you’re welcome to do so! I decided to rather keep the post simple. (E.g. the graphs don’t represent *red* per sΓͺ, red light is quite a bit further right than the peak of the red line. Talking about the “red receptors” is effectively a “mnemonic”.)

  • 2 Pieter // Nov 27, 2008 at 8:20 am

    A monocle! For extra steampunk credit.

  • 3 Charl Botha // Nov 27, 2008 at 10:23 am

    There’s a beautiful item available at tshirthell: πŸ™‚

    On a more serious note: in the (scientific) visualization community, there’s an increasing awareness of these issues. Red-green is unfortunately often used to signify on-off / active-inactive / good-bad, but hopefully we’ll see more instances of more carefully chosen colour palettes.

    I once saw a very interesting keynote by Maureen Stone ( on this matter. She claims it’s unforgivable to use red-green in any user interface. πŸ™‚

    What’s also interesting to note, is that if you take a bunch of outdoor photographs and then run all of that through a principal component analysis, the two highest variance eigenvectors represent red-green and yellow-blue. Evolution is really cool.

  • 4 Die piesangverkoper // Nov 27, 2008 at 10:34 am

    Ek het op my dag ‘n kleurbind holie gehad. Ek moes hom soggens help om sy kleure uit te kies. Maar dit beteken nie hy het swart en wit gesien soos baie mense dink nie. Dit was maar sulke goed soos groen en bruin klere wat hy nie kon onderskei nie en so-aan.

  • 5 Hugo // Nov 27, 2008 at 4:53 pm

    Heh, Charl, that’s evil! What does it say? Maybe I can load it into gimp and look at the channels separately to figure it out. (Or does it say nothing?) Grrrr!

    Now I’m scratching my head about the PCA… care to explain a bit more as to why that would be the case?

    Piesangverkoper… you’re making it too hard for me to pretend I’m uncertain who you are. πŸ˜› As if it wasn’t blatantly obvious. In terme van klere, sit ek dikwels en wonder wat pas wel goed by wat, want ek weet nie eens of dit net “fashion” is en of dit meer objektiewe perspektiewe is wat mens laat weet wat by wat pas nie… (Sekere kleur kombinasies was “uit” ‘n paar dekades terug, maar is tog okei deesdae.)

  • 6 Hugo // Nov 27, 2008 at 4:54 pm

    Oh, also really evil: Swiss payment slips. There’s an orange one and a red one, and I never know whether I am holding and orange or a red. They are insanely close together, being “soft/light red”.

  • 7 Charl Botha // Nov 27, 2008 at 7:20 pm

    It all in this paper:
    D.L. Ruderman, T.W. Cronin, and C.C. Chiao, β€œStatistics of Cone Responses to Natural Images: Implications for Visual Coding,” J. Optical Soc. of America, vol. 15, no. 8, 1998, pp. 2036-2045.

    Comes down to the fact that colour variance in natural scenes can be completely described by three decorrelated axes: red-green, yellow-blue and an achromatic axis.

    So it’s not a why, it’s an observation. The cool thing is that our eyes reflect this observation in that we have achromatic (luminance) receptors and two types of colour receptors: red-green and yellow-blue.

  • 8 Hugo // Nov 27, 2008 at 7:47 pm

    Ah yes, makes sense! I was thinking it was supposed to be related to colour-blindness in some way, but indeed, colour-blindness is absolutely a deficiency.

    Oh, heard anything about octopus eyes? Apparently some of the most advanced eyes on the planet. (Just to undermine any belief in supposed “perfection in the human-eye”, if the blind spot and retina inversion isn’t enough to tip people off.) Picked it up on slashdot a long time ago, saved it away somewhere. I could dig it up and drop it here for anyone interested.

    And I *will yet* find out what that t-shirt says. If it says anything. Grrrr!

  • 9 Hugo // Nov 27, 2008 at 7:51 pm

    Heh, ok, if anyone else is also colour blind, it says what the URL says. Or so they tell me. πŸ˜‰

  • 10 Ben-Jammin' // Nov 27, 2008 at 7:54 pm

    And I *will yet* find out what that t-shirt says. If it says anything.

    Look at the web address – that’s what it says.


  • 11 gerhard // Nov 28, 2008 at 8:54 am

    ehm, do you remember those cheesy 1970s movies? they always portrayed color blind people as wearing these redish amber glasses? same idea. makes the contrast between the two colour greater. Always used to make fun of my uncles pair because they made him look like he was blind thanks to their bulk and lack of design..

  • 12 Hugo // Nov 28, 2008 at 9:09 pm

    I don’t think I’ve seen any of those, no. But if I do, I’ll spot them and grin, thanks!

  • 13 Rinus // Dec 18, 2008 at 3:32 pm


    this reminds me of a colour deficient science teacher we had at school. Not only would we mess with him by implying chemical solutions did NOT become the colour he intended it to be, but some people used to write messages in red chalk on the green board (why do they call those things black boards?)

    It was always amusing how he would start writing equations over the (sometimes not too flattering) messages as if it wasn’t there.

    Yeah, kids really are cruel πŸ˜‰

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